确定哪个 OR 语句选择了记录？

Question

我在criteria 表的记录中保存了条件，我用它来创建一个动态查询字符串，该字符串将查询source 表，该查询的结果将插入到destination 表中.如果条件与source 表中的记录匹配，我的目标是将criteria 表中的ID 插入destination 表中。如果匹配多个条件记录，我只需插入第一个。

WHERE 子句由多个部分OR'ing 构建而成，并且在每个部分中，条件是AND'ed 在一起。类似于以下内容：

insert into destinationTable(col1, col2, col3)
select col1, col2, col3
from sourceTable
where
--' begin generated code'
   (a = 525 and b = 324 and c = 4523) -- 'from criteria record 1'
or (d = 'asdf' and e = 3.43) -- 'from criteria record 2'
or (f = 234523 and g = 9823742) -- 'from criteria record 3'
etc...
--' end generated code'

我需要找到一种方法来确定哪个是第一个匹配条件的 OR 部分，并在目标表中插入相应的条件 id 怎么做？

Answer 1

您可以在 Select 子句中包含一个 case 语句，该语句将输出第一个成功的 OR 子句：

Select ...
    , Case
        When a = 525 And b = 324 And C = 4523 Then Criteria_Row_1_Pk
        When d = 'asdf' and e = 3.43 Then Criteria_Row_2_Pk
        ....
        End As SuccessClausePk

Answer 2

将 or 替换为并集并添加一列给出标准编号

select col1, col2, col3, 1
from sourceTable
where
--' begin generated code'
   (a = 525 and b = 324 and c = 4523) -- 'from criteria record 1'
union all
select col1, col2, col3, 2
from sourceTable
where (d = 'asdf' and e = 3.43) -- 'from criteria record 2'
union all
select col1, col2, col3, 3
from sourceTable
where (f = 234523 and g = 9823742) -- 'from criteria record 3'
etc...

Answer 3

除非可能有一个索引可以为所涉及的所有列提供服务，否则该表很可能会被完全扫描。由于我们要检查所有记录，您不妨在进行过滤之前进行确定。

SELECT col1, col2, col3, Which
FROM
(
    select col1, col2, col3,
    CASE
    --' begin generated code'
    WHEN 
       (a = 525 and b = 324 and c = 4523) -- 'from criteria record 1'
    THEN 1
    WHEN
       (d = 'asdf' and e = 3.43) -- 'from criteria record 2'
    THEN 2
    WHEN
       (f = 234523 and g = 9823742) -- 'from criteria record 3'
    THEN 3
    --' end generated code'
    END Which
    from sourceTable
) SQ
WHERE Which is not null -- remove where it didn't match any criteria

表单是可预测且一致的，足以对代码生成友好